The present invention relates to an extruding device with an extruder cylinder, a screw and a rotary drive for the screw. Advantageously, the extruding device can be used particularly with large single-screw extruders; however, the device may also be used with dual-screw or multi-screw extruders.
Large single-screw extruders can be employed, for example, in LDPE synthesis, meaning in the production of low-density polyethylene, wherein actual production rates can reach 60 tons/hours. Such facilities represent a very large capital investment and are designed with high target operating times in the range of 8000 hours/year. Any longer downtime represents a large economic loss for the operator. Disadvantageously, optionally installed upstream systems, such as crackers, may also have to be shut down when the device fails.
Extruders include typically an extruder cylinder, a screw and a rotary drive for the screw which is rotatably supported in an extruder cylinder. The screw is directly connected to the rotary drive for reliable and low-loss force transmission. The rotary drive may be constructed either with a direct drive or with a motor coupled by way of a gear. In addition, a thrust bearing may be required which absorbs forces resulting from the head pressure. This refers to the pressure exerted on the screw by the melt produced with the extruder. Such thrust bearings may either be integrated in the gear or in the direct drive, or may be provided separately. In the latter case, they are typically arranged between the rotary drive and the extruder cylinder.
In LDPE synthesis, in particular when performed with large single-screw extruders, rotary drives with a gear are typically employed which include various bearings and gear wheels. A thrust bearing, which is generally designed for a predetermined operating time, is arranged between the gear and the extruder cylinder. The operating time is typically in a range of 40,000 operating hours, which includes a statistic failure rate of about 10% for the bearings, i.e. bearings that fail before reaching the nominal operating time.
If a thrust bearing fails or if a gear experiences wear or fails, then the thrust bearing or the gear must be accessible so that the required repairs, for example replacing a gear bearing, can be performed. However, these repairs are quite complicated and can only be performed in multiple process steps.
First, the head end of the extruder must be opened. In an LDPE synthesis, which is typically granulated with a submerged granulator, the entire granulator must be disassembled and moved away from the extruder. The head connection between the extruder and the granulator must be disconnected, the flanges of the transport water loop of the submerged granulator must be opened, the electrical connection of the granulator motor must be disconnected, as well as the wiring of all sensors in the terminal box of the granulator. When the granulator has been axially moved away from the extruder cylinder, the next process step can be performed.
After the head connection of the extruder device has been opened, the screw can be pushed out through the region of the head connection towards the front. This is typically done from the site of the rotary drive through the gear and the thrust bearing, so that the drive-side screw end disengages from the region of the gear and the thrust bearing, i.e., it does no longer protrude into that region.
In particular when no separate shutoff valve for the material to be processed is installed in the extruder device in the region of the feed hopper, problems may arise with the material still remaining in the supply hopper and in the extruder cylinder. Because the material hereby comes into contact with a region of the screw which typically does not contact the material and then contaminates this region, malfunctions may occur later during operation.
When the screw end no longer protrudes into the region of the gear and the thrust bearing, an intermediate housing, which provides a connection between the thrust bearing and the extruder and which is generally divided along its center axis and hence can be opened, can be at least partially removed, so that thereafter the thrust bearing centrally mounted between the rotary drive and the intermediate housing can be removed. Only then can optionally also the gear housing be opened, allowing access to its components. If the malfunction occurs in the region of the thrust bearing, then the aforementioned process steps are also required in order to open the thrust bearing and reach the defective components.
It is therefore an object of the present invention to provide a simple and cost-effective structure which enables easy installation and removal of the individual components and assemblies of an extruding device.